HOW MUCH IS THAT PIGGY IN THE WINDOW?

As Estren sits in the study of his home in McLean talking to a visitor, the snake moves its head slowly along the top of his right shoulder. Reaching the edge of his T-shirt collar, it probes clockwise around his neck, its tongue dancing along the patch of skin below his hairline.

"The tongue is a unique organ in snakes," Estren says. "It's actually like a processor, a microprocessor, of dust from the environment. It carries minute particles of dust into the snake's mouth and brings them to two little organs at the top called Jacobson's organs. And those analyze the environment and tell the snake something about what's there."

An inch shy of Estren's left ear lobe, the snake starts exploring upward again, pushing its nose through the hair on the back of his head. That tickles. Estren smiles and gently grasps the reptile with both hands, unwraps it and allows it to rearrange itself around his right forearm and hand.

Watching this scene, one feels safe in speculating that snake lovers are able to enjoy pleasures elusive to just about everyone else in the world. But Estren, who is an executive vice president for United Press International, says that's not so. According to him, anyone who wants to savor this same arcane joy can do so.

"If you want to invest the time, I think the rewards you get from reptiles are not greater than what you get from cats or dogs, but they're very different," he says. "Reptiles will teach you things about nature and natural processes that you will never learn if you confine yourself to mammals."

In the realm of human animals, Estren belongs to a species (herpetophiles) that's part of a genus (fans of uncommon pets) that's part of a family (pet owners).

Perhaps you're interested in joining his genus, but you don't know the first thing about buying or caring for an uncommon pet. What follows is a primer covering snakes, monkeys, tarantulas, potbellied pigs and ferrets -- all uncommon, but not truly exotic, pets. What's truly exotic? Creatures not practical to raise at home, including anything poisonous, uncageable, wholly untamable or ridiculously large.

All five pet types discussed here can be bought locally from stores and/or breeders, though some are illegal to own in certain areas. Each of the five, in its own way, is pleasurable to nurture as a pet.SNAKES

"I have handled poisonous snakes," Mark Estren says. "I would never keep a poisonous snake as a pet. No matter what anybody tells you, they cannot be defanged, they cannot be 'devenomed,' and they cannot be tamed."

Estren's two snakes -- kingsnake Lear and corn snake Silky -- are constrictors. A constrictor grabs its prey with its teeth, wraps its body around it and squeezes it to death. In this manner Lear and Silky consume mice, each eating from three a week to one every four months.

As a longtime student of herpetology (he also owns five turtles and an alligator-like caiman) Estren always knows when the snakes are hungry.

"Their behavior pattern changes," he says. "They move around differently, they raise their heads and test the air more. You would look at them and say, 'Gee, they're looking for something.' In essence that's correct."

The snakes reside in separate glass aquariums, Silky's resting on a book case and Lear's on a nearby table. Estren can't house them together because bigger and stronger Lear might eat Silky. That could happen on purpose or accidentally, like this: At feeding time, Lear and Silky would simultaneously bite the same mouse. Because snake teeth curve toward the back of the mouth, neither reptile would be able to let go. Lear, forced to swallow a massive meal, would risk death by indigestion.

Silky and Lear, who've been with Estren for 14 and 13 years respectively, are both "rescue jobs," he says. He obtained Silky for a small donation to an animal shelter, and bought Lear for $10 (including an aquarium) from a pet store that was going out of business. Both corn snakes and kingsnakes are indigenous to the United States.

Estren says he hasn't needed to take Lear or Silky to any of the handful of D.C.-area veterinarians who treat reptiles.

"I've never found a vet who knows as much about them as I do," he says. "And I'm not saying that to be boastful. I have in the past had snakes that I've taken to vets, and by the time I finished explaining the behavior changes, which are subtle, the vet has invariably said, 'You know more about this than I do. What do you think it is?' "

Vets who treat snakes generally charge between $25 and $35 for an office visit. The most common snake ailments are respiratory infections, which are usually treatable.

The animals themselves cost anywhere from $2.99 (for a baby garter) to more than $1,000 (for very rare species). Snakes in the $10-$100 range are in good supply at many pet shops in the area. A sturdy aquarium with appropriate furnishings might run from $25 to $175. Most pet stores sell live "feeder" mice for $1.50 to $2.50 apiece.

Classic low-maintenance pets, snakes need little attention beyond feeding and cage cleaning. Cleaning typically takes five to 10 minutes and must be done each time a snake relieves itself, which seldom happens more than once a week.

If there's any drawback to keeping snakes, it's probably that they are notoriously gifted escape artists. A few years ago, during Estren's move to this area from Connecticut, Silky got loose. For the car trip Estren had put her in what he thought was a secure bag, but she found a tiny hole, crawled through it and hid in a dashboard crevice of his Audi 5000.

Two months later, he climbed into the car and saw several inches of Silky dangling from the center console. He knew the only way to rescue her would be to grab firmly and yank. When he did so, Silky bit him three times. He kept holding and comforting her, and within five minutes she calmed down.

Estren retains no illusions about true friendship between him and his reptiles, however. "They get to know your touch," he says. "But the fact of the matter is, they never cuddle you the way a dog does."

Probably that's a good thing for him and every other constrictor owner.

MONKEYS

If snakes are the classic low-maintenance pet, monkeys represent the opposite end of the spectrum. They are expensive, messy, loud, and prone to mental health woes when deprived of the steady company of humans or other monkeys.

"They are colony animals," says Hanna Siemering, a Springfield vet who specializes in uncommon pets. "If you have a monkey all by itself, you've got to be the substitute {for fellow monkeys}. And if you don't have the time, you either have to get another monkey or you need to get rid of this animal."

Or don't buy it in the first place, advises the Humane Society. "Monkeys are totally unsuitable as pets," declares Randall Lockwood, the society's vice president for field services. "Not only do they get many of the diseases humans get, but we get many of the diseases they get."

Add that factor to monkeys' ravenous need of companionship, and you get a pet that most humans can't properly nurture. Says Lockwood, "Virtually all pet primates suffer as a result of their captivity."

Even some happy owners concede that their puny primates can be a pain.

"Wherever he is, he just lets it go," says Kay Dunlap of the excretory habits of her two-year-old tamarin, Trevor. Fortunately, Trevor doesn't have the run of Dunlap's Leesburg house. The one-pound, 10-inch tall monkey stays either in its bedroom or in a cage in the living room.

Dunlap paid $1,500 for Trevor at Landmark Pets in Alexandria, the only local shop licensed to sell monkeys. Landmark's proprietor, Steve Carmody (who recently sold the store), counseled Dunlap about monkeys' need for companionship, and she heeded the advice. She says she spends five to six hours each weekday in Trevor's company -- a substantial commitment, since she works full time outside her home. Her dog, a mixed collie, frolics with the monkey during the day.

Trevor expresses interest in visitors to Dunlap's home, but maintains a rigid hands-off-me policy with everyone besides his keeper. "He'll just kind of sniff at {strangers} and then go on about his business," she says.

At Trevor's bathtime, even Dunlap sometimes has a hard time picking him up. "He'll scream and run away," she says. Thankfully, the pet has never bitten anyone.

Feeding the monkey is a breeze, Dunlap says. Trevor will eat practically anything she serves him, including a specially prepared, canned marmoset food. The canned stuff costs her less than a dollar a week. Vet fees have been nil, as Trevor has never been sick.

The joys of owning the monkey are elemental. He's "fascinating to watch," says Dunlap, who has been enamored of monkeys since she was a tyke. Though she has a special yen for chimpanzees, Dunlap has no desire to own one.

"As dirty as this little one is," she says, "I can't imagine a larger one."

TARANTULAS

Jeff Boyd is a gentle, scholarly fellow who works as a graphic artist and lives in Northern Virginia. In his home he has what he believes is this area's largest private collection of big spiders, but he mainly keeps that information to himself. If his neighbors were to find out they might worry needlessly and maybe even have nightmares.

"A lot of people have an irrational fear of spiders," says Boyd, who owns more than 20 tarantulas, "and they think that they're dangerous. They're not. They're much less dangerous than your house cat or dog. They certainly could not maim you like a cat or a dog."

As he talks, Boyd removes the lid of one of six plastic tubs he's just carried into his living room. Sitting motionless on a bed of sand is an orange-kneed tarantula roughly as wide as a coffee mug. He slips the fingers of both hands underneath the Mexican spider and gently lifts it from its home.

At first, the tarantula appears mildly agitated, moving its legs in a way that suggests a desire to escape. Boyd doesn't restrain it, but places his hands side by side, palms down, and lets the spider walk freely from one to the other. The hands keep shifting -- left-right, right-left -- so that the animal enjoys the sensation of an unbroken walk. Within 30 seconds it seems pacified and begins exploring at a more leisurely pace.

After 10 minutes, he puts the animal back in its shallow tub, and, leaving the lid off, turns his attention to a second spider, a gray one from Thailand. The first one settles into a corner and becomes utterly still. On Boyd's hands, the second spider does exactly what the first one did: walks around rapidly, then settles down.

So it goes for the next hour. One jumbo specimen after another flaunts its splendid behavior for a visitor as the proud owner articulates his arachnophilia.

As a kid he was fascinated by tarantulas, and the allure never ebbed. He bought his first spider when he was in high school and found himself agog over its beauty and its biology, particularly the animal's feeding and molting habits. That first spider lived nine years, he notes proudly.

In spite of its bad-guy (or bad-gal) image, the tarantula suffers stark vulnerabilities.

"They're completely defenseless when they molt," says Boyd. "The hobbyist should never put prey items in with the spider until the cuticles harden {following molting}, because the prey items can actually kill and eat the spider.

"Even a cricket can kill a tarantula when it's in this soft, defenseless state. Normally, a tarantula getting ready to molt in the wild will plug the entrance of its burrow and seal it off so it has a chamber of seclusion, so it can molt without being vulnerable."

Though some of Boyd's large spiders eat only insects, most feed on small, live mice. "Tarantulas hunt by touch," he says. "And when the spider bumps into the mouse, it immediately lunges on it and sinks these huge fangs in and starts puncturing the mouse. It actually kills the mouse before the venom begins to take effect."

Tarantulas rarely bite humans, and even when they do, their venom is roughly as toxic as a bee's.

Other than at meal times, which occur about once every three weeks, spiders seldom stir. "It's not really a pet in a traditional sense," Boyd says. "It's not gonna express any true affection towards you. You can't train it in the same sense as a dog."

Many pet shops do sell spiders, however, generally asking $10-$175, depending on the size and species. So what's to enjoy?

"Plasticity of behavior," he says. "What that means is that all animals somehow can sense and adapt to a situation where they're not being harmed. Any time a tarantula in the wild is being touched by another animal, it's being attacked. So normally a tarantula should not tolerate being touched at all. But yet they do, and they get used to it, so that's a plasticity of behavior."

There's also a physical fragility about the animals that calls for an extremely deft human touch. If a tarantula is dropped, its abdomen typically bursts open. Then, Boyd says, "the spider will either be mortally bruised or its organs will actually pop out and the spider will die shortly thereafter."

If that sounds really gross, consider how such an accident must affect Boyd, who tries to keep each of his spiders healthy for its normal life span of 10 to 30 years.

POTBELLIED PIGS

Maureen Harrigan, a Silver Spring hair stylist whose salon is in her home, acquired a potbellied pig on July 28, 1990. Soon, her business picked up.

Customers started to get their hair done a little more often than they used to. They all wanted to visit with Squiggy, pat his head, scratch his neck, caress his damp little nose. In a small way, the customers were falling in love with the pig. Harrigan knew exactly how they felt. She was doing the same thing in a big way.

"I spent the first week just feeling like I was dreaming," she says one afternoon four weeks after Squiggy's arrival. "Pigs have this natural smile on their faces, and they're just too cute. There's no two ways about it."

A foot tall and 30 pounds heavy, Squiggy is about three-fifths the size he'll be as a full-grown adult. Yet he's already got the moves of an old smoothie. He brushes a flank against Harrigan's calf, gazes up into her eyes and utters a few amorous snorts. She strokes his neck and makes kissing sounds.

Squiggy came to Harrigan from the Posh Pig, a breeding outfit in Sterling, Va. She had been out to Sterling in the spring, had adored the pigs (which are native to Vietnam and China), had desperately wanted to buy one. But the males all cost $1,000 to $1,200, and the females cost $4,000 or more -- roughly the amounts they go for in the few pet shops that have them.

Belinda and Mark Bell, Posh Pig's owners, would have sold her one then for $900, but she didn't have that sum to spare and she just couldn't see adding pig payments to her mortgage and car payments. (Vet and food bills are roughly what they would be for a dog.) Harrigan went home dejected.

Months later, her phone rang. The Bells had just gotten Squiggy back from a customer who'd fallen ill and could no longer care for the animal. Did Harrigan want Squiggy? For free?

Life has been dreamy since then. Squiggy has grown extremely content in his new surroundings. He sleeps in a soft bed under Harrigan's vanity, frolics in a plastic pool in the backyard, plays peacefully with Harrigan's guinea pig, and follows his keeper around the house.

Litter-trained by his previous owner, Squiggy has had only two accidents in his new home. At night he sleeps soundly. And he's definitely not a finicky eater. He takes a combination of pig chow and food scraps (weekly cost: $3), and when in the mood for a snack -- i.e., always -- he stands on his hind legs and accepts hand-fed morsels.

Squiggy's only unexpected behavior has been making strange noises. "He doesn't just oink or grunt," Harrigan says. "He does a certain amount of that. But there are times, particularly when he's playing with the guinea pig, that he tends to soften his voice, and it's more like a little whimper.

"And the same thing when he gets close to my face, when I'm down on the ground playing with him. It's just a gentleness that sets in. It sounds like a whale singing sometimes."

Hog wild. Harrigan has gone hog wild.

FERRETS

If you have an infant, do not get a ferret.

Even ferret proponents concede that the pert little critters love the smells and tastes of milk, lotion and powder, and generally will gnaw the face of a prone baby if given the chance. Several such attacks have been documented in recent years, so the infant-safety issue isn't even open to quibbling.

What's worth discussing is whether ferrets are okay for adults to own. The Humane Society says no, because the animals -- which resemble tapered squirrels with lovely, cat-like coats -- are insufficiently domesticated and sometimes rabid.

Veterinarians generally take the opposite view. "They're safe," says Hanna Siemering, a Springfield vet. "I see lots of ferrets, about 15 to 20 a week, and probably in the last year there have been four of them that have tried to bite. That's an incredibly low number. For cats, it would be about four a month."

As for rabies, Siemering notes that a rabies vaccine for ferrets became available earlier this year. Also, she says, "Ferrets are house animals, so they cannot get rabies except from the bite of a rabid animal. And you don't have raccoons and skunks running through your house, so the chances of domestic ferrets getting rabies are extremely low."

A minor but noteworthy point of contention is ferrets' musky smell, which can offend the noses of owners and non-owners alike. Happily, the glands that produce this odor can be surgically removed. Pet stores typically sell only neutered and "de-scented" ferrets -- usually priced at $100 to $175 -- while breeders typically sell "unfixed" animals for around $85 (unless an animal has unusual markings, which can make it worth upwards of $300). Many vets do treat ferrets, charging $20 to $30 per checkup.

Meticulous housekeepers, beware. "Ferrets can be destructive," says Kim Gilbert of Annandale, the happy owner of three. "They tend to get into things like trash cans and knock 'em over. They're not necessarily chewers, but they're very mischievous and their curiosity levels are incredible. They get up on my mantelpiece, on top of my fish tank. They can climb, they can jump. They can get to places you never thought they could get to."

For all their shortcomings, ferrets remain popular in America. The Roanoke, Va.-based International Ferret Association claims over 100,000 members. People like the animals because they're cute, exuberant and very friendly to humans and other house pets. Also, they can be litter-trained as easily as cats.

"They have excellent personalities," says Gilbert. "Cats tend to keep to themselves, but ferrets are just so affectionate and playful. Everything I do around the house, they follow me around, right on my heels. I can't do a thing without them being underfoot."

Gilbert says her ferrets sleep on her lap and come running to greet her when she opens the front door.

Many puppies will do that kind of stuff, of course, but puppies have the disadvantage of always turning into dogs. And dogs have the drawback of being comparatively laid-back and, at least in the mind of the uncommon-pet fan, common.

LOCAL PET RESTRICTIONS

D.C. residents may not own pigs or ferrets.

ALEXANDRIA residents may not own pigs.

ARLINGTON COUNTY residents may not own pigs.

PRINCE GEORGE'S COUNTY residents who want to own either a monkey or a pig must apply for a permit. For information call 925-6160.

FAIRFAX COUNTY residents may not own monkeys or pigs, but pigs may be allowed in the near future. For information on pending pig legislation, call Barbara Snow at 830-3680.

MONTGOMERY COUNTY doesn't restrict the ownership of any of the five pets discussed above.

Kevin McManus last wrote for Weekend about tours of Washington workplaces.